In each of general electronic devices and optical devices, a sealing material of some kind is required in order to protect a semiconductor chip, which becomes the core of the device, and wiring. In a light emitting element which outwardly outputs an optical signal, or in an optical sensor which detects external light, particularly, the sealing material not only protects the semiconductor chip but also has an important role of fixing in some form a lens and an optical window which are used for derivation or introduction of light. In particular, in the case of a highly sensitive optical sensor, which detects a weak signal, the package of the sensor is designed so as to have the function of stabilizing the temperature of the sensing element, or blocking external electromagnetic noises against the sensing element. On the other hand, in order to produce a miniature device, while the size of a semiconductor chip should be made smaller, the package thereof should also be made smaller within the extent that performance of the device is not deteriorated.
In these manners, a lot of contrivances have been applied to a package of an optical device, in order to obtain a maximum performance in light detection sensitivity or light emission efficiency, which is an essential function of the optical device, while minimizing and simplifying the package. To achieve miniaturization of the package as a whole, packages using sealing resin is often used.
In each of general electronic devices other than optical devices, it is possible to obtain a very highly reliable package fabricated by using a mold because neither derivation nor introduction of light is necessary. On the other hand, in the case of an optical device, it is necessary to provide a optical window for derivation or introduction of light.
However, in a case where a optical window is formed by designing a mold such that the a window can be formed, and by performing a sealing step with the mold, it has been difficult to provide an adequate optical window aperture. This is because burrs of sealing resin inevitably remain on the optical window after the sealing step is performed, obstructing the light passage.
Additionally, in the case of attempting to form the optical window after a molding step with a sealing material, it is necessary to open a hole in the sealing material in some way. For example, in the case of attempting to perform etching so as to open a hole in the sealing material by a sandblasting method, the optical device may also possibly be destroyed.
For example, Patent Document 1 discloses a mold for providing a optical window of an optical device to a miniature package covered with a sealing material. Specifically, inside of this mold, provided is an elastic body configured to be into contact under pressure with the front face of the optical window of the element which detects light, and accordingly the mold prevents the sealing material from entering the optical window of the element during a sealing step. On this optical window, a light blocking film having a pinhole to determine the direction of entrance or exiting of light is formed. Accordingly, a large portion of light entering the optical window is blocked not by the sealing material but by the light blocking film, and only a part of the entering light enters the pinhole. Hence, desired light detected by the element which detects light does not pass through the entire face of the optical window.
Here, if a method disclosed in Patent Document 1 is used, since the elastic body is pressed in the sealing step on the element which detects light, and the element may possibly be broken. Additionally, burrs of the sealing elements remain on the optical window in some cases, and it is necessary to perform a step of removing burrs by a physical etching method or the like in order to form a desired optical window aperture. For this reason, there has been a problem where reliability of manufacturing steps becomes low. Because burrs of the sealing material enter the optical window from a periphery thereof toward a central element thereof in the sealing step, especially, darkening due to burrs is a serious problem in a case where the optical window needs to transmit light with a high transmittance. Furthermore, in a case where the optical window is provided with a function of adjusting the intensities of light input and output, it is impossible to use the step of removing burrs because the optical device could be destroyed. This results in a problem of extremely low productivity.
On the other hand, it is necessary to provide some kind of optical window for an infrared sensor which detects light in the infrared region (for example, light having long wavelengths of 5 to 10 microns). This is because there is no resin material that efficiently transmits the infrared light having long wavelengths, and thus because an epoxy resin package used for an infrared sensor which detects infrared light of not more than about 1 micron, cannot be directly used. For this reason, in a conventional infrared sensor, it is necessary to use a hollow package or a metal package to provide, apart from a sensor element, an optical window material capable of efficiently transmitting light so that sensitivity of the sensor would not be reduced. However, there has been a problem that utilization of a hollow package makes it difficult to miniaturize the sensor, and also, complicates assembly.
Additionally, miniaturization of an infrared sensor for long wavelengths has not been possible so far because it is necessary to enlarge the area and the volume of a photoelectric conversion portion in an infrared sensor for long wavelengths so as to obtain a high S/N ratio, and also because it has been necessary to provide a cooling unit even in the case of a quantum type sensor which is said to be highly sensitive.
Likewise, in an ultraviolet sensor which detects ultraviolet light having wavelengths of not more than 300 nm, it is necessary to use a optical window material made of quartz glass, sapphire glass or the like because ultraviolet light cannot pass through an epoxy resin that allows visual light to pass there through and is used in a photodiode for visual light and the like. Accordingly, fabrication of an optical device that is miniature and is easy to package has not been possible. Thus, an application range of ultraviolet sensors has been limited.
Next, in the case of an infrared sensor which normally outputs weak signals, a circuit which processes the output signal from the sensor becomes necessary in addition to a photoelectric conversion portion. In such a case, the output signal from the infrared sensor comes to function as a sensor after going through an amplification circuit and a circuit which performs comparison processing, and is generally composed of pluralities of resistance components, capacity components, signal processing circuits, and the like. Accordingly, a range of utilization of infrared sensors has been limited for such reasons that miniaturization of the size of a sensor is difficult if a element corresponding to the signal processing circuits is included in the size in addition to the sensor composed of a metal package, and that the number of manufacturing steps is large.
In response to this, as is disclosed in Patent Document 2, a method of attempting miniaturization by additionally packing a signal processing circuit into a metal package has been proposed. However, also in this method, there is a problem that reduction in size and thickness is difficult because it is necessary to avoid influence of heat between a pyroelectric sensor and the signal processing circuit obtained by integrating signal processing circuits including an amplification circuit as a core; and to provide a optical window material that efficiently transmits infrared light having long wavelengths.
Accordingly, conventional optical devices have a problem that they cannot be miniaturized for restrictions on the package of the sensor.
Patent Document 1: Japanese Patent Laid-open No. Hei6-77526
Patent Document 2: Japanese Patent Laid-open No. Hei9-288004
Patent Document 3: International Publication Number WO2005/027228